1. Field of the Invention
The present invention relates generally to a digital circuit for formatting and compressing video data. More particularly, the present invention relates to a digital circuit which includes a data compression engine for compressing digital video data received from a missile in flight and a frame formatter for formatting the compressed video data prior to transmission from the missile.
2. Description of the Prior Art
Radar video data received from a missile in flight is a wide bandwidth signal that exceeds the bandwidth limitations of the missile""s telemeter, which is the signal transmitter for the missile. Typically, a signal of this type has a bandwidth in the vicinity of 20 megahertz. To properly analyze the operation of a missile which transmits radar video data, every radar scan needs to be transmitted by the missile to a receiving station.
In addition, the receiving station generally does not have the capability of handling signals which have a bandwidth in the vicinity of 20 megahertz.
Further, for military applications there is generally a requirement that the radar video data be encrypted which means the radar video data must be digitized. Employing a digital resolution of at least six bits increases the bandwidth requirements to at least 120 megahertz. This is far beyond the capabilities of any receiving station currently in use.
Currently, there are no known technologies which will accurately and completely transmit all the radar video data captured by a missile in flight. Technologies previously considered to reduce the bandwidth of the signal transmitted by a missile include scan skipping which sends out one out of every ten radar scans, scan averaging and lossy compressions which are compressions greater than four to one. These technologies for transmitting radar video data are not acceptable to the military which requires a complete and accurate transmission of the data in order to analyze the missile""s performance during a test flight.
The present invention overcomes some of the difficulties of the prior art including those mentioned above in that it comprises a highly effective and efficient digital circuit for compressing video data generated by a missile""s seeker prior to the missile""s telemeter transmitting the compressed data to a remotely located ground station. The digital circuit includes a frame controller and data compression circuit or video compression engine. The frame controller generates each frame of data with each frame of data comprising eight subframes. Each subframe generated by the frame controller has a length of one thousand eight bit words.
The compression engine receives approximately sixty four scans of video data from the missile""s seeker with each scan having 4000 samples of video data. The compression engine receives the first scan of video data from the missile""s seeker and then writes the scan of video data to an external memory which is a static RAM. The compression engine adds each successive scan of video data to the previous scans to provide a total scan value for each sample of video data. The compression engine then processes the total scan value of each sample of video data to provide an average value for each sample of video data. The average value for each sample of video data is obtained by performing a binary shift which shifts the data six places to the right.
The compression engine also provides a peak value for each of the 4000 samples of video data. The compression engine compares each of the 4000 samples of video data with a corresponding sample of video data stored in the external memory and then writes the sample of video data having the largest value into the external memory.
The frame controller then generates the eight subframes of video data with alternating eight bit words comprising peak video data and average video data. The frame controller also provides control data comprising three bytes of frame sync, one byte of sub-frame identification and one byte representing frame count. One byte representing scan count for each subframe of video data is generated by the compression engine.